Social History: Zora recently lost her job due to frequent tardiness as a result of oversleeping after bouts of insomnia.

Family History: Zora’s father has severe Delayed Sleep Phase Disorder.

Review of Sleep Pattern: A sleep log kept for the past six months shows that Zora experiences a relatively regular alternation between 8 days of normal sleep and 8 days of sleep-onset difficulties. During the latter cycle, she lies in bed for 4 to 6 hours before she is able to fall asleep. Zora cannot identify any reason for these episodes of poor sleep.

Evaluation and Diagnosis: Zora wore a wrist actigraph for 10 days to monitor her activity levels; in addition, repeated measurements of plasma levels of melatonin were taken for use as a circadian phase marker. In addition, for a period of five weeks, Zora was asked to go to bed and get up whenever she felt like it. During this time, her sleep disorder vanished entirely. Zora went to sleep and woke up naturally about 4 hours later each day than on the previous one, indicating that her circadian rhythm was too long to be entrained into the 24-hour circadian rhythm. She was diagnosed with Non-24 -Hour Sleep Wake Disorder (Non-24).

Treatment and Follow-up: Over a period of 10-week, Zora attempted to entrain her circadian rhythm; she exposed herself to 2 hours of bright light in the morning, and took 3 mg of melatonin at bedtime. This was unsuccessful and Zora’s sleep difficulties did not improve.

She then discovered that she was successful when she followed her own internal sleep-wake schedule, as she had done during the diagnosis process. She now sleeps when she is tired, regardless of the time of day or night.

Using the sleep log, enabled Zora to track her sleep-wake cycle and identify patterns; she can now predict her sleep-wake cycle for two or three weeks in advance. This allows her to work successfully as a freelance journalist when she is awake, and make daytime appointments only when she can anticipate that she will be awake that day.